1. Field of the Invention
The present invention relates, in general, to a method for the fabrication of liquid crystal display device and, more particularly, to a method for the fabrication of a liquid crystal display device which is preventive of damage to a gate electrode of the liquid crystal display device by a chemical etchant.
2. Description of the Prior Art
In order to better understand the background of the present invention, a description will be made of a conventional fabrication method of a liquid crystal display device, in conjunction with FIGS. 1 through 4.
First, referring to FIG. 1, there is shown a pattern of a gate employed in a conventional thin film transistor. As shown in this figure, the conventional liquid crystal display device comprises a glass substrate 1 on which a gate metallization 10, a gate pad 20 and a gate line 25 are formed in their own patterns with the gate metallization having an electrical connection with the gate line 25 through the gate pad 20. In FIG. 1, the numeral 30 designates a display region.
After fabrication of the liquid crystal display shown in FIG. 1, it is necessary to cleave an area A of FIG. 1, which is connected with an anodized oxide line, for testing the liquid crystal display device. Generally, the area A is formed in the same manner as that employed for fabricating the liquid crystal display device and thus, at same time.
Referring now to FIGS. 2 and 3, there are illustrated a conventional process for fabricating a liquid crystal display device and a process for cleaving an area connected with an anodized oxide line, respectively.
Firstly, as shown in FIG. 2A and FIG. 3A, aluminum or aluminum-tantalum is deposited under vacuum at a predetermined thickness on a glass substrate 1 using a sputtering process and is then subjected to photolithography to form a gate electrode 2.
Secondly, as shown in FIG. 2B and FIG. 3B, the gate electrode 2 atop the glass substrate 1 is immersed in an electrolytic solution and subjected to an electric field, to form an oxide layer 3 which results from reaction of a portion of the gate electrode 2 with the electrolytic solution.
Thirdly, as shown in FIG. 2C and FIG. 3C, an insulation material, such as SiN.sub.X or SiO.sub.X, is deposited on the oxide layer 3 by a chemical vapor deposition process, to form a gate insulation film 4, followed by sequential formation of an active layer 5 and an impurity-doped layer 6. For the active layer 5, amorphous silicon (a-Si:H) is deposited on the gate insulation layer 4 by a plasma enhancement chemical vapor deposition process. For the impurity-doped layer 6, amorphous silicon doped with high density impurities (n.sup.+ -a-Si:H) is deposited, in the same process.
Subsequently, in case of the fabrication process of liquid crystal display device, the impurity-doped layer 6 is patterned, as shown in FIG. 2D. On the other hand, in case of the cleavage process, the impurity-doped layer 6 and the active layer 5 were in sequence selectively removed, as shown in FIG. 3D.
In the cleaving process, a pad process is undertaken to form a lead line for wire-bonding as well as to remove the gate insulation layer 4 selectively. As a result, the gate insulation layer 4 is removed at the area with which an anodized oxide line is connected, and a pattern of photoresist and a PR is formed, as shown in FIGS. 3E and 3F.
Thereafter, as shown in FIG. 2E and FIG. 3G, indium tin oxide (hereinafter referred to as "ITO") is deposited on the resulting structure and then etched by a chemical etchant, to form a transparent electrode 7.
Next, as shown in FIG. 2F and FIG. 3H, aluminum is deposited under a vacuum over the transparent electrode 7 in a sputtering process and then subjected to photolithography, to form a source/drain electrode 8.
A cleaving testing process step is undertaken to separate the gate electrode 2 at an area connected with the anodized oxide line, as shown in FIG. 3I.
However, a serious problem may arise prior to cleaving the gate electrode 2 at the connected area when using the conventional method. With reference to FIGS. 4A and 4B, there is shown a damage region 2a of the gate electrode caused by the chemical etchant. As shown in these figures, the gate electrode 2 may come into contact with the chemical etchant prior to being cleaved. That is, the gate may be etched by the chemical etchant when the transparent electrode 7 is formed by the wet etch process. Since the gate electrode 2 is made of aluminum or aluminum-tantalum, which is rapidly etched, it is easily damaged by the chemical etchant.